In a train radio system in which an operation of a train is controlled by communication between an on-board device of the train and a ground device, it is required that the on-board device detects the position of the train and the position of the train in an area is managed. When some trouble occurs in an operation of a train, the train cannot be displaced to a rail yard, and so the train sometimes has to be retained or stayed overnight on a railway track. However, when movement due to wandering or rolling motion occurs during retainment or overnight stay of the train, the train moves in a condition in which a power source of on-board devices of the train is turned off, thereby making a difference between position information stored in the on-board device of the train before the power source of the on-board device is turned off and an actual on-rail position of the train. It is noted that the wandering motion means movement of a stopped vehicle in which a vehicle power supply is turned off, which is caused by the vehicle allowed to move because an on-rail position of the train is on a slope, and the rolling motion means movement of a stopped vehicle in which a vehicle power supply is turned off, which is caused by the vehicle allowed to move due to a problem on how brakes have been put thereon. If an operation of a train is started in such a situation that the position information stored in the on-board device of the train and the actual on-rail position of the train are different from each other as described above, the on-board device cannot recognize an accurate distance between its own train on which the on-board device is mounted and another train, so that the train radio system cannot be operated satisfactorily. This problem may also occur not only in a case of the wandering or rolling motion but also in a case where a train is hauled to be displaced. Haul/hauling means to move a vehicle whose vehicle power supply is turned off, by pulling the vehicle using another vehicle.
Patent Literature 1 that is an example of a conventional technique discloses a train management system in which a train on a railroad in each of sections obtained by dividing a rail track into parts is managed on a ground side based on train identification information transmitted from a train ID oscillator mounted on the train, and a boundary between the sections is provided with an ID detecting device that detects the train identification information. According to the technique of Patent Literature 1, the train ID oscillator and the ID detecting device constantly perform communication with each other, so that an accurate on-rail position of the train can be recognized.